A technique in which a display device arranged on the user's vehicle displays information about a moving object by using a mark or letters has been proposed. The technique is used for informing a user of the approach of the moving object to the user's vehicle.
For example, an information providing device disclosed in Patent Literature 1 identifies a vehicle that is likely to the approach to the user's vehicle. The device displays the identified vehicle with an icon, changes a size of the icon in accordance with a distance between the user's vehicle and the identified vehicle, and changes a stripe pattern which is a background image of the icon, in accordance with a speed of the identified vehicle. Thereby, the user can intuitively recognize the approach of the identified vehicle to the user's vehicle.
Patent Literature 2 discloses a driving support apparatus that displays a mark having an arrow shape representing either degree of approaching of another target vehicle to the user's vehicle or degree of leaving of another target vehicle from the user's vehicle when the target vehicle is located obliquely behind the user's vehicle.
In this apparatus, a guide line is displayed in addition to the mark having the arrow shape. The guide line indicates the risk to the user's vehicle due to the target vehicle traveling on a lane adjacent to the user's vehicle when the user's vehicle tries to move to the adjacent lane. For example, when the target vehicle is approaching the user's vehicle at a relatively high speed, the mark representing a movement of the target vehicle, which is a relatively long arrow toward the user's vehicle, is displayed such that the relatively long arrow is across the guide line. With such a display, the user can recognize that lane-change of the user's vehicle is risky because the target vehicle is approaching the user's vehicle.